Communicating with Charts

Data Visualisation Workshop

Nicola Rennie
1 November 2023

Introduction

This session will include:

  • why you should visualise data;

  • some guidelines for making better charts;

  • examples of charts made in R;

  • a chance for you to make charts!

RSS Data Visualisation Guide

royal-statistical-society.github.io/datavisguide

Screenshot of data vis guide homepage

Why visualise data?

Data visualisation has two main purposes:

  • Exploratory data analysis and identifying data issues
  • Communicating insights and results

Examples of sequential, diverging, and qualitative palettes

Exploratory data visualisation

Because summary statistics aren’t enough…

Dataset A B
mean_x 54.2632732 54.2658818
mean_y 47.8322528 47.8314957
sd_x 16.7651420 16.7688527
sd_y 26.9354035 26.9386081
cor_xy -0.0644719 -0.0686092

Communicating insights with data visualisation

Grab attention

Visualisations stand out. If a reader is short on time or uncertain about whether a document is of interest, an attention-grabbing visualisation may entice them to start reading.

Improve access to information

Textual descriptions can be lengthy and hard to read, and are frequently less precise than a visual depiction showing data points and axes.

Summarise content

Visual displays allow for summarising complex textual content, aiding the reader in memorising key points.

Communicating insights with data visualisation

John Snow collected data on cholera deaths and created a visualisation where the number of deaths was represented by the height of a bar at the corresponding address in London.

This visualisation showed that the deaths clustered around Broad Street, which helped identify the cause of the cholera transmission, the Broad Street water pump.

Snow. 1854.

John Snow cholera map

Tips for better charts

Choosing a chart type

What is the purpose of the chart?

Try: ft-interactive.github.io/visual-vocabulary

Screenshot of visual vocabulary website

Why do people hate pie charts?

Taylor Swift hate gif

Source: giphy.com

Why do people hate pie charts?

Why do people hate pie charts?

The Sun front page showing the Boris Johnson pie chart

Elements of charts

  • Layout
  • Aspect ratio
  • Lines
  • Points
  • Colours
  • Axes
  • Symbols
  • Legends
  • Orientation
  • Auxiliary elements
  • Dimensionality

Layouts, aspect ratios, and axes

Layouts, aspect ratios, and axes

Layouts, aspect ratios, and axes

Layouts, aspect ratios, and axes

Should the y axis start at 0?

Layouts, aspect ratios, and axes

They don’t always have to start at zero…

Layouts, aspect ratios, and axes

Order categories appropriately…

Layouts, aspect ratios, and axes

Order based on magnitude unless the category order has meaning…

Badly ordered chart of covid cases

Source: Georgia Department of Public Health

Lines

  • Suggest an order
  • Suggest continuity

Colours

Why use colours in data visualisation?

  • Colours should serve a purpose, e.g. discerning groups of data

  • Colours can highlight or emphasise parts of your data.

  • Not always the most effective for, e.g. communicating differences between variables.

Colours

Different types of colour palettes…


… for different types of data.

Examples of sequential, diverging, and qualitative palettes

Colours

Is this a good choice of colour?

Colours

Check for colourblind friendly plots with colorblindr::cvd_grid(g).

Colours

  • In base R via {RColorBrewer}: brewer.pal(4, "Dark2")

  • In {ggplot2}, scale_fill_brewer(), scale_fill_distiller(), scale_colour_brewer(), scale_fcolour_distiller().

  • Alternatives to theme_grey()!

Screenshot of colorbrewer2.org

colorbrewer2.org

Legends

  • Should not use up valuable space for data
  • May be integrated into the figure

Legends

or use {ggtext} to colour font in the subtitle…

Line chart of stick performance

Fonts

Arial: Does it pass the 1Il test?


Times New Roman: Does it pass the 1Il test?


Courier New: Does it pass the 1Il test?

Fonts

  • Font size: larger fonts are (usually) better

  • Font colour: ensure sufficient contrast

  • Font face: highlight text using bold font, avoid italics

  • Font family: choose a clear font with distinguishable features (pick something familiar)

There is no perfect font.

Key points

  • Charts should have a purpose

  • Actively design visualisations

  • Default settings aren’t always the best choices

Useful resources

TidyTuesday logo

Good charts don’t have to be boring!

Stacked diverging bar chart of lego colours

Cara Thompson (cararthompson.com)

small multiples are charts of college basketball

Cedric Scherer (cedricscherer.com)

Good charts don’t have to be boring!

Supreme court justice chart

Tanya Shapiro (tanyaviz.com)

Sloped area chart

Dan Oehm (gradientdescending.com)

Your turn!

Discussion

This data set is from a study published in 1757 in A Treatise on the Scurvy in Three Parts, by James Lind.

“Pages 149-153 are a rare gem among what can be generously described as 400+ pages of evidence-free blathering, and these 4 pages may represent the first report of a controlled clinical trial.”

study_id treatment dosing_regimen_for_scurvy gum_rot_d6 skin_sores_d6 weakness_of_the_knees_d6 lassitude_d6 fit_for_duty_d6
001 cider 1 quart per day 2_moderate 2_moderate 2_moderate 2_moderate 0_no
002 cider 1 quart per day 2_moderate 1_mild 2_moderate 3_severe 0_no
003 dilute_sulfuric_acid 25 drops of elixir of vitriol, three times a day 1_mild 3_severe 3_severe 3_severe 0_no
004 dilute_sulfuric_acid 25 drops of elixir of vitriol, three times a day 2_moderate 3_severe 3_severe 3_severe 0_no
005 vinegar two spoonfuls, three times daily 3_severe 3_severe 3_severe 3_severe 0_no
006 vinegar two spoonfuls, three times daily 3_severe 3_severe 3_severe 3_severe 0_no
007 sea_water half pint daily 3_severe 3_severe 3_severe 3_severe 0_no
008 sea_water half pint daily 3_severe 3_severe 3_severe 3_severe 0_no
009 citrus two lemons and an orange daily 1_mild 1_mild 0_none 1_mild 0_no
010 citrus two lemons and an orange daily 0_none 0_none 0_none 0_none 1_yes
011 purgative_mixture a nutmeg-sized paste of garlic, mustard seed, horseradish, balsam of Peru, and gum myrrh three times a day 3_severe 3_severe 3_severe 3_severe 0_no
012 purgative_mixture a nutmeg-sized paste of garlic, mustard seed, horseradish, balsam of Peru, and gum myrrh three times a day 3_severe 3_severe 3_severe 3_severe 0_no

Discussion

Edit the code to improve this chart:

library(ggplot2)
library(medicaldata)
data("scurvy")

ggplot(data = scurvy) +
  geom_col(mapping = aes(
    x = study_id,
    y = gum_rot_d6,
    fill = treatment
  )) +
  theme(legend.position = "bottom")

15:00

Discussion

Bring your own chart! (Or make a new one!)

Data sources:

Gif of labrador painting

Source: giphy.com

Workshop resources

GitHub: github.com/nrennie/chicas-data-viz-workshop


Slides: nrennie.github.io/chicas-data-viz-workshop


Questions?

n.rennie@lancaster.ac.uk

nrennie.github.io/chicas-data-viz-workshop